FIG. 1 depicts a prior art Sagnac sensor array (SSA) system 1 comprising a source 3, a coupler 5 having input ports 7A-7C and output ports 9A-9C, a clockwise distribution and agglomeration bus A, a counterclockwise distribution and agglomeration bus C, clockwise channel couplers 15A(1)-15A(N−1) where N−1=2, counter clockwise channel couplers 15C(1)-15C(N−1) where N−1=2, rungs R1-RN, sensors 17(1)-17(N), and detectors 19F and 19G. Reference to the 3rd rung as the N rung is intended to show that the actual number of rungs may vary between different sensor arrays.
In the SSA system 1, a signal 21 comprising a series of pulses of light is generated by the intensity modulated source 3 coupled to the 3×3 optical coupler 5. The coupler 5 splits the signal 21 equally among the three output ports 9A, 9B, and 9C, such that each pulse of the signal 21 output by the source 3 is split into a clockwise (cw) pulse, signal 21A, traveling along bus A, and a counter clock wise (ccw) pulse, signal 21C, traveling along bus C. The cw and ccw signals 21A and 21C travel down the busses A and C until they encounter couplers 15A(1) and 15C(1) that each split off a portion of the signals 21A and 21C, and cause the split off portions to traverse the rung R1, and the non-split off portions to continue down the busses A and C. The non-split off portions continue until they reach the next set of couplers, 15A(2) and 15C(2), that each split off a portion of the signals reaching them, and cause the split off portions to traverse the rung R2. This splitting of the remaining portions of signals 21A and 21C continues on until a final rung RN is reached at which point signal 21A has been split into a plurality of signals 21A(R1)-21A(N) and signal 21C has been split into a plurality of signals 21C(R1)-31C(N). As can be seen, the busses A and C each comprise a plurality of linearly arranged channels coupled together by the couplers 15A and 15C.
When the split off portions 21A(R1)-21A(RN) and 21C(R1)-21C(RN) of the signals 21A and 21C traverse the rungs R1-RN, they are modified by sensors 17(1)-17(N) of the rungs R1-RN. As shown, the split off portions 21A(R1)-21A(RN) are designated 21F(R1)-21F(RN) after passing through the sensors 17(1)-17(N), and the split off portions 21C(R1)-21C(RN) are designated 21G(R1)-21G(RN) after passing through the sensors 17(1)-17(N). On exiting the sensors 17(1)-17(N), the signals 21F(R1)-21F(RN) are combined on bus C by the couplers 15C(1)-15C(N) to form signal 21F, and the signals 21G(R1)-21G(RN) are combined on the bus A by the couplers 15A(1)-15A(N) to form signal 21G.
Because each pulse of the signals 21A and 21C is delayed by a coil 6 (21C after it passes through the sensors to become 21G), and split between rungs, each pulse of the signals 21A and 21C becomes multiple pulses in the signals 21F and 21G with the increased number of pulses being proportional to the number of rungs R1-RN in the SSA system 1. The individual pulses in the signals 21F and 21G are independent from each other, with each pulse in signal 21F carrying sensed information obtained via a sensor in a particular sensor rung, and each pulse in signal 21G carrying sensed information obtained via a sensor in a particular sensor rung.
The signals 21F and 21G are combined in the 3×3 coupler 5. The timing of the individual pulses of the signals 21F and 21G are such that both the cw and ccw pulses corresponding to an input pulse that passed through a particular rung pass through the coupler 5 at the same time. As a result, the pulses for a particular rung interfere with each other. The resultant signals 21F′ and 21G′ exiting the ports 7A and 7C are detected by the detectors 19F and 19G with the detected signals being used to obtain information imparted by the sensors 17(1)-17(N).
There is a limit to the number of sensors/rungs a sensor system such as the SSA system 1 can include before running into signal to noise issues. This is due at least in part because of the need to divide the cw and ccw signals among all the sensors/rungs. Unfortunately, having a limit on the number of sensors limits the amount of area the SSA system 1 can cover. Having a limit on the number of sensors also limits the sensing capabilities of the SSA system 1.
For later discussion, the portion of the SSA system 1 to the right of coupler 5 will be referred to as the “ladder” or “SSA ladder” of the SSA system 1. As can be seen, the ladder 31 of SSA system 1 includes the pair of buses A and C, and the rungs R1-RN extending between the busses A and C, and the sensors of those rungs. The SSA ladder 31 also includes a delay coil 6. However, “ladders” and “SSA ladders”, as the terms are used in the detailed description, do not necessarily include a delay coil.